An ink-jet head for recording a desired image by jetting ink from nozzles onto a recording medium is maintained, to be able to jet ink in a normal state all the time, in such a manner that: ink is periodically and forcibly subjected to suction from nozzles; thus high viscosity ink accumulated in nozzles is exhausted; and thereby blockage in nozzles is resolved.
To suck ink as described above, it is necessary to cause a suction cap to tightly contact with the nozzle surface of the ink-jet head. However, the nozzle plate of an ink-jet head is extremely small, and even a nozzle plate having several hundreds of nozzles has dimensions, for example, 1 cm multiplied by several cm, or the like. Accordingly, when ink is sucked from nozzles, there are problems in that the nozzles cannot be covered with a suction cap enough, that, even when the nozzles are covered with the suction cap, the suction cap does not contact with the nozzles tight enough to ensure airtight, and so on. Further, although the nozzle plate is bonded to the front end of an actuator, the gap between the nozzle plate and the recording medium is so small as approximately 1 mm. Therefore, if the recording medium has come in contact with the ink-jet-head, a paper jam may occur on the recording medium and a large force may be applied to the head, which peels the nozzle plate off the actuator. Therefore, with respect to an ink-jet head, enclosing the periphery of a nozzle plate by a front plate is carried out to prevent these problems.
Thus, an ink-jet head is arranged in such a way that a nozzle surface is located in an opening of a front plate formed in a flat plate shape having the opening. By this front plate, the surface of a nozzle plate is protected; peeling of the nozzle plate is protected; and a space large enough to allow tight contact of a suction cap with the nozzle plate is formed.
However, if the front plate encloses the nozzle plate, ink gathers at the joint edge between the nozzle plate and the front plate. In this situation, although ink on the nozzle surface of the ink-jet head can be removed by wiping with a blade, the nozzle surface is desirably arranged at a position, in the opening of the front plate, deeper than the position of the surface of the front plate in order to prevent damage of nozzles due to, for example, rubbing with the recording medium. However, if nozzle surface 100a is arranged in a deeper position (the lower side in the figure) in opening 111 than surface 110a of front plate 110, ink 200 and dust easily gather at the joint edge between nozzle plate 100 and the front plate 110. Accordingly, wiping of the nozzle surface 100a cannot be performed effectively. Further, if the ink 200 having gathered here touches with a nozzle 101, problems such as disturbance of ink jetting and the like occur.
On the other hand, as shown in FIG. 6, if the nozzle surface 100a is arranged protruding from the surface 110a of the front plate 110, even when ink 200 or dusts gather at the joint edge between the nozzle plate 100 and the front plate 110, since the ink 200 or the dusts do not come in contact with the nozzle 101, ink jetting cannot be disturbed. However, since the nozzle surface 100a is protruding from the surface 110a of the front plate 110, the nozzle surface 100a cannot be protected, which causes problems of scratching the water repellent surface and peeling the nozzle plate 100.
For example, Patent Document 1, described later, discloses a technology in which a head cap for protection of a nozzle plate is arranged enclosing the nozzle plate, the nozzle surface is positioned 2 to 20 μm deeper than the surface of the head cap so that a blade and a recording medium do not come in hard contact with the nozzle surface, and thus a water repellent film coated on the nozzle surface can be prevented from peeling.
Further, Patent Document 2, described later, discloses a technology in which a nozzle plate cover is arranged around the periphery of a nozzle plate, the nozzle surface is positioned protruding toward a recording medium from the nozzle plate cover by the height not greater than the thickness of the plate, and thus the nozzle plate is prevented from peeling.
Still further, Patent Document 3, described later, discloses a technology in which, as shown in FIG. 7, in the state that nozzle surface 100a is protruded from surface 110a of front plate 110, adhesive 300 is applied to the edge space therebetween, then, an actuator is drawn back to move the nozzle surface 100a to a deeper position than the surface 110a of the front plate 110, and in this state, the adhesive 300 is cured. Thus, the step generated between the nozzle surface 100a and opening 111 of the front plate 110 is smoothed by the adhesive 300 to reduce ink that remains after cleaning by a blade.
(Patent Document 1) TOKKAI No. 2000-141652
(Patent Document 2) TOKKAI No. 2001-150668
(Patent Document 3) Patent No. 3127573
In the technology disclosed in Patent Document 1, as the nozzle surface is drawn to a position a little deeper than the surface of the front plate, the nozzle surface is protected. However, as a step is generated between the nozzle surface and the surface of the front plate, when removing ink adhering to the nozzle surface by wiping, ink tends to gather in the step, which may cause ink jetting failure due to the contact of the gathering ink with nozzles.
In the technology disclosed in Patent Document 2, although ink does not gather on the nozzle surface since the nozzle surface is protruded a little from the surface of the front plate, the nozzle surface cannot be protected enough.
In the technology disclosed in Patent Document 3, there is a problem that adhesive tends to flow into nozzles. To prevent this flow in of the adhesive, painstaking mask treatment is required, and further, to stably form the shape of the adhesive, it is necessary to finely control the relative position between the nozzle surface and the front plate after applying the adhesive, according to various conditions including the characteristics of the adhesive, the environmental temperature, and the dimensions of the gap between the nozzle surface and the opening of the front plate, which causes a problem of extreme difficulty in control of the adhesive and the shape thereof.
The defect common to the above technologies is that it is impossible to prevent ink from gathering at the joint edge between an actuator and a front plate, because an opening having a rectangular cross-section with dimensions which the actuator just fits in is formed through the front plate, and the actuator is inserted in the opening.